General Ruger graduated from West Point in 1854. He was practicing law in Janesville, Wisconsin, at the beginning of the Civil war, and in 1861 was commissioned lieutenant-colonel of the Third Regiment Wisconsin Volunteers. He served with conspicuous gallantry and rose to the rank of brigadier-general and brevet major-general of volunteers, and was brevetted brigadier-general in the regular army for gallantry at Gettysburg. He was commissioned colonel in the regular army in 1866; superintendent of the West Point Military Academy, 1871-76; commissioned brigadier-general, 1896; in 1891 in command of the Department of California with headquarters at San Francisco; later in command of the Department of the Missouri, headquarters at Chicago; retired in 1897.